The present invention relates to a doctor arrangement for roll presses which includes a web transfer device which lies against the barrel surfaces of each of the respective rolls or against a wire mounted on the barrel surface.
A roll press generally includes two mutually coacting press rolls that define a press roll nip therebetween. The rolls are arranged in a trough into which a suspension of material, such as a pulp suspension, is delivered. The rolls have liquid pervious barrel surfaces and the suspension is de-watered by pressing the liquid through these surfaces with the aid of an overpressure. Final de-watering of the suspension to a desired dry content of the material is achieved in the nip between the rolls. The barrel surfaces of the press rolls comprise perforated sheet metal attached to a roll body. In order to obtain a sufficiently large capacity, the combined open area of the holes must be large while, at the same time, the holes must be small so that fibers will not accompany the liquid through the holes. Wires may be mounted onto the barrel surfaces of the rolls for this purpose. Downstream of the roll nip a doctor arrangement is located which functions to remove the de-watered pulp web from the rolls or from the wires mounted thereon. The doctor arrangement includes a web transfer device for each roll. In the past, the web transfer device has comprised a doctor beam that includes a doctor blade for abutment with the barrel surface of the roll or with the wire.
The present invention is based upon a problem which was encountered with doctor beams and doctor blades. This problem is one of maintaining the doctor blade and the wire surface at a particular distance apart, and is particularly manifested by the greater lengths of such roll presses. With the intention of obtaining maximum possible rigidity, the doctor beam has been provided with a box-like construction. The boxlike construction, coupled with the temperature differences of the different plates in the beam structure, make it impossible to retain the doctor blade setting. Consequently, the doctor blade has been placed firmly against the roll in practice, in order to reduce fiber transfer in the pulp. In the case of presses that do not include wires, this practice has been more or less successful, and results in lower fiber transfer. In the case of rolls that are fitted with wires, however, it has not been possible to adjust the doctor blade to a zero setting without the risk of cutting the wire to pieces.
An object of the present invention is to thus eliminate the aforesaid problem and to enable the doctor blades to optimally abut the press rolls.
In accordance with the present invention, this and other objects have now been realized by the invention of apparatus for handling a web comprising a pair of juxtaposed press rolls including an outer surface and providing a nip therebetween for providing the web, a coarse shredder trough disposed above the nip for receiving the web from the nip, web transfer means for transferring the web from the outer surfaces of the pair of juxtaposed press rolls, and web transfer means comprising a plurality of doctor sections extending longitudinally of the pair of juxtaposed press rolls and a plurality of doctor blades attached to the plurality of doctor sections and extending in abutment with the outer surfaces of the pair of juxtaposed press rolls, the web transfer means being supported by the coarse shredder trough by a pair of adjustable support members and a pair of pivot shafts for pivotable movement of said pair of adjustable members. In accordance with a preferred embodiment, the outer surfaces of the pair of juxtaposed press rolls comprise wire means mounted on the outer surface of the pair of juxtaposed press rolls.
In another embodiment, the pair of adjustable support members comprises a pair of bottle screws.
In accordance with one embodiment of the apparatus of the present invention, the pair of adjustable support members comprises spring means for resiliently mounting the pair of doctor sections relative to the outer surface of the pair of juxtaposed press rolls. In a preferred embodiment, the spring means are adjustable into a rigid position with respect to the outer surface of the pair of juxtaposed press rolls.
In accordance with another embodiment of the apparatus of the present invention, the apparatus includes suspension means connecting the coarse shredder trough with the plurality of doctor sections at the intersection of the plurality of doctor sections, the suspension means also connecting the plurality of doctor sections together at the intersection. Preferably, the suspension means is eccentrically pivotably connected to the plurality of doctor sections.